Problem: Stephanie is 4 times as old as Umaima and is also 12 years older than Umaima. How old is Stephanie?
Explanation: We can use the given information to write down two equations that describe the ages of Stephanie and Umaima. Let Stephanie's current age be $s$ and Umaima's current age be $u$ $s = 4u$ $s = u + 12$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $s$ is to solve the second equation for $u$ and substitute that value into the first equation. Solving our second equation for $u$ , we get: $u = s - 12$ . Substituting this into our first equation, we get the equation: $s = 4$ $(s - 12)$ which combines the information about $s$ from both of our original equations. Simplifying the right side of this equation, we get: $s = 4s - 48$ Solving for $s$ , we get: $3 s = 48$ $s = 16$.